1. Field of the Invention
The invention relates to a method and apparatus for clearing gas bubbles from the pumping chamber of a bellows or positive displacement pump. In particular, the invention relates to a method and apparatus for clearing gas bubbles from a fluid reservoir and from the pumping chamber of a single valve positive displacement pump. The invention has specific application to clearing gas bubbles from an implantable or external medication infusion pump.
2. Description of the Contemporary and/or Prior Art
With the acceptance of both external and implantable infusion devices, researchers have been attempting to develop a pump which satisfies the strict performance requirements imposed on those devices. Research indicates that the positive displacement pump, such as a bellows pump, appears to be the most attractive type of pump for infusion devices. However, if even small gas bubbles enter into the pumping chamber of a bellows or positive displacement pump, the amount of fluid delivered per stroke (the stroke volume) will decrease. A significant gas bubble entering such a pump will stop the pumping of an incompressible liquid altogether, because the gas bubble can expand and/or compress before sufficient pressure is generated to open the inlet and/or the outlet valve(s).
Prior art references attempt to solve this problem by providing a filter means which prevents gas bubbles from entering the chamber. U.S. Pat. No. 4,191,181, issued to Manfred Franetzkion, on Mar. 4, 1981, attempts to solve this problem by using a wick like member composed of lightly packed glasslike fibers which have sufficient capillary forces to prevent gas from entering the fine channels. Similarly, U.S. Pat. No. 4,360,019, issued to Portner et al, attempts to solve this problem by using a looped tube that terminates a short distance from the side of the straight portion of the tube. This distance is smaller than the diameter of air bubbles, thus blocking their entry into the tube.
However, the prior art does not teach a method or apparatus for removing a gas bubble once it has found its way into the pumping chamber.